Australian medical staff have been moved to safety on Manus Island after a security incident involving PNG agencies on Friday morning.

The Minister for Immigration and Border Protection Scott Morrison confirmed the international health and medical services staff at the detention centre had to be moved for their own safety but he refused to reveal what had happened.

Mr Morrison only revealed the information about the incident after being questioned about tweets from the Asylum Seeker Resource Centre reporting that employees were evacuated due to security concerns.

"There was an incident earlier today on Manus Island and appropriate steps were taken to ensure staff were placed in safety," Mr Morrison said.

The Immigration Minister refused to elaborate further saying it is a matter for the PNG government.

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Mr Morrison told reporters that the staff had been evacuated to a nearby naval vessel, but he was forced to put out a statement after the briefing saying he had been misinformed.

In the statement, he said he had since been told no staff had been removed to the HMAS Choules.

He said that the Department of Immigration and Border Protection and its service providers took appropriate measures to ensure the safety of staff and transferees.

''The government can confirm that no transferees were under threat during this incident and that none were harmed,'' Mr Morrison said in a statement.

Mr Morrison was speaking at a weekly briefing on immigration and border security where he also denied reports that there were two women, pregnant with twins currently in detention on Nauru.

He said the reports about the women being pregnant with twins was ‘‘conjecture’’ and he said it was not true.

Sovereign Borders operational commander, Lieutenant General Angus Campbell, said three boats with 173 people on board had arrived in the past week.

He told the briefing that one boat had arrived with 79 Sri Lankans on board. He said none of them had reasons to seek refuge in Australia and 73 had already been returned to Sri Lanka.

Lieutenant Campbell said the remaining six were having health checks to assess their suitability to be flown home.

The briefing was told there are currently 1061 people on Manus Island, 827 on Nauru and 2211 on Christmas Island.